Higher concentrations of pollutant particles could amplify the waves of coronavirus contamination, scientists have suggested and may explain, in part, the geographic profile of the Covid-19 pandemic.
The correlation between fine particulate matter and the severity of influenza waves is said to be well known to epidemiologists.
Fine particles, also known as PM2.5 have an aerodynamic diameter less than or equal to 2.5 micrometers and are produced from combustion processes, vehicles and industrial sources.
Glasgow is among the UK cities with the highest levels of PM2. 5s in the country, with a concentration of 16 micrograms per cubic metre.
Researchers from the University of Geneva (UNIGE) investigated possible interactions between acutely elevated levels of fine particulate matter and the virulence of the coronavirus disease.
Covid-19 studies carried out in Italy and France suggest that Covid-19 was already present in Europe at the end of 2019, while the sharp increase in morbidity and mortality was only recorded in spring 2020 in Paris and London.
Mario Rohrer, a Swiss climatologist, who was also involved in the study, said this suggests something else was at play.
He said: "This time lag is surprising, but also suggests that something else than just the mere interaction of people may promote the transmission of the virus, and particularly the severity of the infection."
His research team has been able to show that these increases in cases followed phases where the levels of fine particles in the air were higher.
The team made similar observations in the Swiss canton of Ticino, where fine-particle pollution increased sharply during a period of shallow fog on the Magadino plain and the Sotto Ceneri, observed at the end of February 2020.
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Shortly afterwards, an explosive increase in hospital admissions due to Covid-19 was recorded in Ticino. The fact that a large carnival event with some 150,000 visitors took place at the same time probably had an additional impact on the spread of the virus, said Mr Rohrer.
The information is important for Switzerland because the increase in fine particle concentrations is particularly frequent during thermal inversions, ie when fog forms on the Swiss Plateau, thus limiting the exchange of air masses.
In these situations, emissions accumulate in the layer of air underneath the fog. Switzerland is also frequently swept by dust from Saharan sandstorms, also pointed out in this study.
The Swiss research team shows that acute concentrations of fine particles, especially those smaller than 2.5 micrometers, cause inflammation of the respiratory, pulmonary and cardiovascular tracts and thicken the blood. In combination with a viral infection, these inflammatory factors can lead to a serious progression of the disease.
Inflammation also promotes the attachment of the virus to cells and the coronavirus may also be transported by the fine particles.
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This has already been demonstrated for influenza and an Italian study found coronavirus RNA on fine particles. "All this remains to be demonstrated, of course, but it is a likely possibility," added Mr Roher.
The researchers said that although particulate matter pollution can influence the virulence of the virus and possible severe disease progression, physiological, social or economic factors will clearly also influence the further course of the pandemic.
Mario Rohrer said the study offer the possibility of taking preventive measures in the event of future increases in fine particulate matter concentrations to try to limit a new flare-up of Covid-19 morbidity and mortality.
Their results are published in the journal Earth Systems and Environment.
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